There exist various types of hand-operated fluid and paste material dispensing devices of the caulking gun variety which include a plunger adapted to advance axially through a cylinder to which the end of a paste material cartridge is attached. The plunger is advanced by a trigger-type lever pivoted to a pistol grip, and a ratchet device is mounted to the end of the lever for engaging a rod forming part of the plunger.
Examples of such devices include caulking guns, grease guns, cookie guns, bone cement dispensing guns, and the like. These various fluid extrusion and dispensing devices are disclosed in the patent literature, for example, in U.S. Pat. Nos. 4,994,065; 4,356,938; 1,846,167; 1,672,421 and United Kingdom Patent No. 905,049.
With respect to caulking guns, caulking guns are designed to extrude caulking compound by use of a piston and ratchet-type mechanism. When the amount of the caulking compound desired has been discharged from the caulking gun, forward movement of the piston is stopped, and the piston is held in place by the ratchet mechanism which prevents any backward movement. The caulking compound, being elastic and relatively high viscosity, is in a compressive state and continues to flow out of the caulking gun. The continuing flow of compound frequently creates a mess in addition to being a waste of material.
Most caulking guns have some type of pressure release mechanism. To release the pressure in the typical caulking gun, the gun is equipped with a ratchet bar having teeth along one side only, so that the rod may be turned and rotated about its axis. When the rod is turned, the ratchet teeth are no longer held by the ratchet mechanism and the piston is allowed to move freely backward. This method of relieving the pressure in the caulking gun requires the use of two hands, one to hold the gun, and one to turn the ratchet bar. In most instances, the flow of compound from the caulking gun is not stopped immediately by this method since time is needed to reach and turn the ratchet bar.
In the prior art there are several patents which provide for pressure relief in the caulking gun without having to turn the ratchet bar. They are:
Good U.S. Pat. No. 2,367,347 PA1 Peterson 2,530,359 PA1 Collins 2,889,085 PA1 Subwick 4,126,251 PA1 Crewe U.S. Pat. No. 2,180,987 PA1 Crewe 2,229,839 PA1 Crewe 2,233,587 PA1 Crewe 2,367,346
In all of these patents, the pressure relief mechanism is not activated automatically, but requires some action by the operator.
There are also several patents in the prior art which show mechanisms that relieve pressure in the caulking gun without requiring any affirmative action by the operator. These patents are:
All of the prior art patents mentioned immediately above fully relieve the pressure in the caulking gun when the operator releases his grip on the lever, except the Crewe, U.S. Pat. No. 2,233,587 which relieves the pressure in the caulking gun when the lever is fully squeezed. Fully relieving the pressure automatically in a caulking gun results in having to reestablish sufficient pressure to force the caulk out of gun. Thus, the operator will have to squeeze the operating lever many more times to discharge a desired amount of caulk.